Particular combustion systems for gas turbine engines utilize combustors having bundled tube type fuel nozzles for premixing a gaseous fuel with compressed air upstream from a combustion zone. A bundled tube type fuel nozzle assembly generally includes multiple tubes that extend through a fuel plenum body which is at least partially defined by a forward plate, an aft plate and an outer sleeve. Compressed air flows into an inlet portion of each tube. Fuel from the fuel plenum is injected into each tube where it premixes with the compressed air before it is routed into the combustion zone.
A portion of each tube may be rigidly connected to the aft plate while a downstream end or tip portion is unconstrained, i.e., each tube is cantilevered from the aft plate. The downstream end or tip portion of each tube extends through a corresponding tube opening defined in a cap plate which is axially spaced from the aft plate of the fuel plenum body and positioned proximate to the combustion chamber. A circumferentially continuous radial gap is defined between an outer surface of each tube at its tip portion and the corresponding tube opening in the cap plate to allow for a cooling fluid, such as compressed air, to flow around the tube towards the combustion chamber, thereby cooling the tip portion. During operation, combustion dynamics may cause oscillation of the various components resulting in undesirable impacts between the components and increased wear thereof, e.g., the tip portion of each tube may vibrate within the gap potentially resulting in undesirable contact between the individual tubes and the cap plate.